In widely used electrophotographic image forming apparatuses, for example, a paper sheet is conveyed to an image forming unit where an image is formed on the paper sheet. An image forming apparatus of this type typically includes a device to detachably attach a paper sheet stacking tray to the image forming apparatus body, and automatically carry a paper sheet stored in the paper sheet stacking tray to the image forming unit. The paper sheet stacking tray used in an image forming apparatus of this type can store paper sheets of various sizes in a single tray. Specifically, an image forming apparatus of this type includes a trailing end regulating device that regulates an upstream side of the paper sheet in the conveying direction, and a width regulating device that regulates a position of the paper sheet in the width direction crosses perpendicularly the conveyance direction, in a manner such that the positions thereof can be changed depending on the size of the placed paper sheet.
Various sizes of the paper sheets typically are paper sheets of predetermined sizes defined by the standards (hereafter, referred to as paper of standard size). For example, paper sheets of standard sizes such as DIN-A4, DIN-A3, 8.5×11 inches, and 11×17 inches, and paper sheets out of these standard sizes (hereafter, referred to as paper of non-standard size) are used widely.
A user who uses these various paper sheets may place a paper sheet on a paper sheet stacking tray after fixing the width regulating device and the trailing end regulating device at predetermined positions, or place a paper sheet in advance on the paper sheet stacking tray, and fix the width regulating device and the trailing end regulating device depending on the size of the paper sheet.
In an apparatus in which paper of standard size is used, in order to make the user easily operate the width regulating device and the trailing end regulating device, labels or stamps may be provided at positions corresponding to the sizes of the paper of standard size to indicate desired positions of the regulating device. Further, clicking and the like at the time of regulating the device operation may indicate that the regulating device is located at a desired position.
However, in a case where the paper of standard size is used, even if a width regulating device by a user, or a configuration to make an operation of die trailing end regulating device easy is provided, the operation thereof is not necessarily made as intended by the user. That is, since different users interpret visually aligning the position of the regulating device with indication, such as a label and a stamp, or clicking at the time of operating the regulating device slightly differently from one another, a case in which the regulating device is fixed while being shifted slightly from a desired position is also known.
For example, if the trailing end regulating device is placed at a position at which the length of the paper sheet in the longitudinal direction from the desired position is reduced, the paper sheet is pressed by the regulating device more than necessary, and the leading end and the trailing end of the paper sheet becomes closer to each other. This causes the following problems: the paper sheets are not lifted by a swing type lift plate due to friction between the leading end of the paper sheet and a wall of an end of the tray; or paper feeding failure is caused by lift pressure loss.
If the trailing end regulating device is placed at a position at which the length of the paper sheet in the longitudinal direction from the desired position is increased, the leading end position of the paper sheet on the paper sheet stacking tray may also be changed from the desired position and, therefore, the relative position between the leading end position of the paper sheet and the feed roller which conveys the paper sheet may be changed. This may cause paper feeding failure such as failure in conveyance.
Then, as disclosed in PTL 1, a fixing position of paper of standard size is made noticeable by removing a positioning shape of a trailing end regulating device at a boundary between a position corresponding to paper of standard size and a position corresponding to paper of non-standard size to help a user easily find an ideal position for the trailing end regulating device when using paper of standard size. In the configuration of PTL 1, however, there has been a case where the trailing end regulating device is positioned by neither a positioning mechanism for standard size nor a positioning mechanism for non-standard size near the position corresponding to paper of standard size. If the trailing end regulating device is used while being shifted slightly, the position of the regulating device is not fixed at the region where positioning shape of the regulating device has been removed. Therefore, the following problems may be caused: the position of the regulating device is changed while the paper sheet is being fed and, thereby, sheet skew may be caused.